1. Field of the Invention
This invention relates to a device for measuring displacement, and more particularly to a device which is useful as a level sensor.
2. Description of the Prior Art
A conventional level sensor is known, for monitoring increases in a conductive liquid delivered into a tank.
Namely, a pair of sensor elements each comprised of electrode portions and resistor portions formed one after another are provided within the tank, wherein the electrode portions are adapted so that they can come into an electrical contact with a liquid whose liquid level changes, and the resistor portions are coated on their surfaces with an insulating material so that they do not come into an electrical contact with the liquid.
A power supply voltage is applied to one sensor element. Further, the other sensor element is connected to a buffer amplifier and is grounded through a resistor from the junction of the other sensor element and the buffer amplifier.
In the level sensor thus constructed, an input voltage of the buffer amplifier rises stepwise with rising of the liquid level.
An output voltage of the buffer amplifier is inputted to a large number of comparators connected in parallel and is compared with reference voltages at the respective comparators.
The reference voltages of the comparators are set so that they have potentials slightly lower than the step potentials of the output voltage of the buffer amplifier, respectively.
Thus, as the level of the liquid rises, outputs of respective comparators shift to "H" level in order from the comparator having the lowest reference voltage to comparators having higher reference voltages.
Outputs from respective comparators are inputted to a priority encoder, at which they are converted to binary codes, respectively.
An output from the priority encoder is inputted to, e.g., a display or a microcomputer, etc.
Thus, the increases in a conductive liquid delivered to the tank is monitored.
The characteristics of the sensor elements are deteriorated because of contact with the liquid, and it is therefore necessary to often exchange them.
Since the resistor portions of the sensor element have unevenness, however, the characteristic is changed upon replacement of the sensor element. Namely, when a sensor element is exchanged, the characteristic of the output voltage of the buffer amplifier does not necessarily show a step potential slightly higher than the reference voltage of each comparator.
Thus, it is inconvenient to use the previous reference voltages as they are, so new reference voltages must be set, resulting in the problem that such a setting is troublesome.